In progress is a behavioral-developmental-longevity study of C3H mice that were sham radiated or microwave radiated in utero (three exposures between 9th and 15th days of gestation: 2.45-GHz at 60-Hz sine modulation, 43-mW/g whole-body dose rate for 20-min. in a multi-mode cavity; dams' LD% equals 10). Twelve months have elapsed since inception of the study; the folloing observations have been made: 1) mortality of radiated pups of surviving dams was higher than that of controls, but there is little difference to date in death rates of weaned animals; and 2) indices of development (e.g., eye-opening latency, growth of pelt, body mass) have been essentially the same for radiated and control animals. Of particular interest in the coming months will be differences, if any, of longevity of animals and of rate of development of spontaneous tumors in this mammary-tumor-prone strain of mouse.